- The Glycemic Index is used to measure how a particular food affects the blood sugar level of an individual and how quickly and to what degree it causes the blood sugar level to rise. The index relies upon its measurement of levels of carbohydrates in foods, as other substances do not have the same substantial effects upon the body and blood sugar levels as do carbohydrates. A GI rating of 100 is reserved for foods such as white bread, and it is these foods and their high rating of 100 by which other foods are rated. In any particular food, a number of factors will determine whether it receives a GI rating that is low, high or medium. Salt in foods, of course, has a profound affect on the GI level, as the rate of digestion of these foods due to the salt is hiked significantly. Foods with high fiber content contribute to differing GI levels thanks to a slower effect on blood sugar due to slower digestive effects. Acidic qualities of foods, whether natural or added, decrease the GI of a meal thanks, again, to slower digestion, and items that are riper carry a higher glycemic index.
- The particular glycemic index of a food can be figured out by any number of experiments, but some rules and designs inherent to these experiments are all shared. A suitable sample size of test subjects-generally at least 10-are subjected to any number of foods containing at least 50 grams of available carbohydrates. Test-size portions of each particular food vary because 50 grams of digestible carbohydrates come in different sized portions in different foods. Once test foods are chosen, each subject has a sample of blood taken from her body at regular intervals before and after consuming the test foods. Generally, this is every 15 minutes during the first hour and every 30 minutes following this initial hour.
- The reference food in all this, the independent variable, is 50 grams of pure glucose. Once a volunteer eats the suggested foods, her blood sugar levels are compared to her blood sugar levels when taken following the consumption of the pure glucose. The average blood sugar response to any particular food is compared to this pure glucose level, and from there the particular food's GI index is determined. Generally, it takes a couple of weeks from start to finish to test a food's GI index.
